In general, the processing of silver halide photographic materials comprises the steps of development, fixing (or bleach-fixing) and washing.
Development is made by processing the light-exposed photographic material in an aqueous alkaline solution (composition) containing a developing agent.
In general, the developer solution, in addition to the developing agent, comprises other organic or inorganic compounds useful to improve its characteristics.
For example, aqueous alkaline developer solutions for preparing photographic black and white images with silver halide photographic materials (i.e. black and white developer solutions), in addition to developing agents (such as hydroquinone or a hydroquinone derivative), comprise auxiliary developing agents, antioxidants (such as alkaline metal sulfites), buffering agents, organic antifogging agents and inorganic or organic alkaline compounds.
Aqueous alkaline developer solutions for preparing photographic color images with silver halide photographic materials associated with image dye-forming couplers (i.e. color developer solutions), in addition to developing agents (such as p-phenylene diamine derivatives) comprise organic and inorganic antifogging agents, antioxidants (alkaline metal sulfites, hydroxylamine salts), buffering agents (such as borate, carbonate, phosphate salts) and inorganic or organic alkaline compounds.
In addition the above mentioned ingredients, both color and black-and-white developer solutions comprise sequestering agents which are capable of both preventing deposit formation and also increasing resistance to oxidation.
It is well-known that insoluble calcareous deposits, which damage photographic materials and processing apparatus, are formed if hard water due to the presence of Ca.sup.++ and Mg.sup.++ ions is used in the preparation of developer solutions. The presence of sequestering agents capable of complexing said polyvalent metal ions prevents said deposits from being formed.
Traces of other metal ions, such as iron and copper (which have been introduced into the developer solutions as impurities contained in water and chemical compounds used in developer solutions) are also known to have a catalytic effect on aerial oxidation of developing agents. Said metal ions, in the case of color developer solutions, have also the effect of catalyzing the decomposition of hydroxylamine salts used as antioxidants and causing adverse sensitometric effects. The addition of sequestering agents capable of complexing Fe.sup.++ and Cu.sup.++ ions has therefore the object of stabilizing the photographic developer solutions.
Nevertheless, a good sequestering agent for photographic developer solutions is difficult to find. As a matter of fact, sequestering agents useful in black and white developer solutions are not as effective in color developer solutions. Moreover, the use of sequestering agents in color developer solutions, containing hydroxylamine salts, presents considerable difficulties because such sequestering agents often tend to decompose the hydroxylamine salts. Still moreover, sequestering agents may negatively affect the sensitometric characteristics of the photographic materials processed in the developer solutions containing such sequestering agents.
Therefore, there is the need of overcoming said restrictions in the use of sequestering agents in photographic developer solutions and providing sequestering agents which make developer solutions resistant to aerial oxidation and deposit formation and can be used both in black and white developer solutions and in color developer solutions, particularly in the presence of hydroxylamine salts.
Research Disclosure 18837 describes various classes of sequestering agents such as polyphosphonic acid sequestering agents of the following formulas:
(1) amino-N,N-dimethylenephosphonic acids of the formula EQU R.sub.3 --N(CH.sub.2 PO.sub.3 M.sub.2).sub.2 PA1 wherein M is a hydrogen atom or a monovalent cation and R.sub.3 is an alkyl group, an aryl group, an aralkyl group, an alkaryl group, an alicyclic group or a heterocyclic radical, and R.sub.3 can be further substituted with substituents such as hydroxyl, halogen, an alkoxy group, a --PO.sub.3 M.sub.2 group, a --CH.sub.2 PO.sub.3 M.sub.2 group, or an --N(CH.sub.2 PO.sub.3 M.sub.2).sub.2 group; PA1 (2) hydroxyalkylidene diphosphonic acids of the formula ##STR1## in which R.sub.4 is an alkyl group, preferably of one to five carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, and the like; PA1 (3) aminodiphosphonic acids of the formula ##STR2## in which R.sub.5 is an alkyl group, preferably of one to five carbon atoms; and PA1 (4) N-acyl-aminodiphosphonic acids of the formula ##STR3## where R.sub.6, R.sub.7 and R.sub.8 are hydrogen or an alkyl group, preferably alkyl of one to five carbon atoms.
U.S. Pat. No. 4,596,764 describes specific aminopolyphosphonic acid sequestering agents for use in color developers, namely: 1,3-diaminopropanol-N,N,N',N'-tetramethylenephosphonic acid, ethylenediamine-N,N,N',N'-tetramethylenephosphonic acid and 1,3-propylenediamine-N,N,N',N'-tetramethylenephosphonic acid.